Geoffrey Lean is Britain's longest-serving environmental correspondent, having pioneered reporting on the subject almost 40 years ago.

Warming brings chilling news from the Arctic

The Arctic ice coverage reached a record low last September. (Photo: AFP)

What is happening on the roof of the world? New research to be published in the Journal of Geophysical Research suggests that there was less ice in the Arctic last September than at any time in recorded history – and this month may set a new low record for its extent.

The news will reawaken fears that global warming is melting the Arctic ice cap far faster than scientists had expected. The concern ignited in September 2007 when the ice cover shrank to 4.13 sq km, less than 60 per cent of the lowest level in the early 1970s, and an alarming half a million sq km smaller than the previous record two years before. (The ice reaches its annual minimum in September, after the northern summer, before increasing again with the onset of colder autumn temperatures.)

The news shocked scientists because the Intergovernmental Panel on Climate Change had not expected the ice to retreat so far until around 2050. But the next two years were a little better, allowing some sceptics to claim that the ice was recovering, even though it remained well below the long-term 1979 – 2000 average. In June last year the ice cover dipped below what it had been in that month in 2007 but, nevertheless, ended slightly higher in September. But the new research, carried out by scientists at Washington University – which has attempted to measure its thickness as well as its extent – concludes that in September 2010 there was, in fact, less ice in the Arctic than ever before.

Such an estimate is inevitably less exact than those that just measure the extent of the ice, which can be done by satellite. Though some measurements are made of thickness, much has to be estimated by computer modeling: indeed the paper is even cautiously entitled “Uncertainties in modeled Arctic sea ice volume’. But they nevertheless conclude that the amount of ice fell “by a large enough margin to establish a statistically significant new record.”

This year may also yet prove to be a record breaker. As the month opened – with about two weeks of the melting season to go – the extent of the ice was almost exactly the same as it was at the same stage in 2007, after having shadowed that so-far unsurpassed year since May; it was lower in early July, then did rather better , but the rate of loss has recently accelerated. And the National Snow and Ice Data Center in Boulder Colorado reckons that its volume has also been below 2007 levels, at least until July.